Duplicating switch for streaming data units to a terminal

ABSTRACT

Streaming to a terminal by using a duplicating switch to receive a stream of data units, using the duplicating switch to store content from the stream, using the duplicating switch to generate a second stream that incorporates the content that was stored and address information corresponding to more than one terminal whose addressing information was not part of the first stream, and using the duplicating switch to make the second stream of data units available to two or more terminals.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/090,727, filed Mar. 6, 2002, and titled “A DUPLICATING SWITCH FORSTREAMING DATA UNITS TO A TERMINAL”, now allowed, which claims priorityfrom U.S. Provisional Application No. 60/343,183, filed Dec. 31, 2001,and titled “A DUPLICATING SWITCH FOR STREAMING DATA UNITS TO ATERMINAL”, and which is a continuation-in-part of U.S. application Ser.No. 09/893,692, filed Jun. 29, 2001, and titled “GENERATING MULTIPLEDATA STREAMS FROM A SINGLE DATA SOURCE”; now allowed, which claimspriority from U.S. Provisional Application No. 60/286,964, filed Apr.30, 2001, and titled “GENERATING MULTIPLE DATA STREAMS FROM A SINGLEDATA SOURCE”. The entire contents of the prior applications areincorporated herein in their entirety.

TECHNICAL FIELD

This application relates generally to streaming media.

BACKGROUND

The term multimedia streaming describes a process for allowing access tomultimedia content from one or more sources. Increased usage of theInternet has resulted in an increased demand for multimedia streaming.

SUMMARY

In one general aspect, data units may be streamed to a terminal by usinga duplicating switch to receive a first stream of data units, storecontent from the first stream, generate second streams that incorporatethe stored content, and make the second streams available to theterminals.

Implementations may include one or more of the following features. Forexample, using the duplicating switch to store content may includestoring content that is temporally related to the data units that arebeing generated. A location identifier may be used to indicate whichportion of content is being generated into the second streams. Locationidentifiers may be used to access the content time-shifted as twodifferent streams. Using the duplicating switch to store content alsomay include storing more than one instance of the same portion ofcontent, and storing additional instances of the stream as demand forthe content increases.

Using the duplicating switch to store content may include storingcontent and associated header information. Using the duplicating switchto store content also may include storing a checksum describing thecontent.

A second stream may be transmitted in response to receiving a requestfrom a terminal or a service provider. Storing the content may includeusing location identifiers to track simultaneous transmissions of asingle stored instance of a stream, and making streams available mayinclude transmitting the different data units within the single storedinstance to several requestors who have terminals receiving the streamthat overlap but differ by a time differential. The duplicating switchmay be a specialized device including hardware configured to perform oneor more of receiving a first stream of data units, storing content fromthe first stream, generating second streams, and making the secondstreams available.

Other features and advantages will be apparent from the followingdescription, including the drawings, and the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a communications system capable of using aduplicating switch to generate a stream of data units.

FIG. 2 is an exemplary component diagram of a duplicating switchsuitable for use in the communications system of FIG. 1.

FIG. 3A is an exemplary block diagram of a duplicating switch that usesmemory (e.g., RAM (“Random Access Memory”)) to store a media stream forsubsequent playback.

FIG. 3B is an exemplary block diagram of a duplicating switch that usesstorage to store a media stream for subsequent playback.

FIG. 4 is a block diagram of a precoder for use in a duplicating switch.

FIG. 5 is a flow chart of a procedure for processing a received dataunit using a duplicating switch in a communications system, such as thecommunications system of FIG. 1.

FIG. 6 is a flow chart of a procedure for providing a stream of dataunits in a communications system, such as the communications system ofin FIG. 1.

FIG. 7A illustrates a duplicating switch structured and arranged tostore multiple instances of a stream of data units.

FIG. 7B illustrates a duplicating switch structured and arranged tostore multiple location identifiers.

FIG. 8 is a flow chart of a procedure for time-shifting content in acommunications system, such as the communications system of FIG. 1.

Like reference symbols in the various drawings may indicate likeelements.

DETAILED DESCRIPTION

Generally, a duplicating switch receives a source stream of data unitsand stores content of the stream to enable subsequent generation of oneor more streams that incorporate the content. Storing the contentpermits time shifting of the content for subsequent transmission. Forexample, an on-demand system can be created to transmit stored contentfrom a source stream in response to a user's request. The duplicatingswitch may use one or more pointers to enable simultaneous access todifferent portions of content from the same source stream and thussimultaneous generation of several different and offset streams from asingle source stream. The duplicating switch may store multipleinstances of content from a source stream to manage increased demand.The duplicating switch also may reduce overall storage requirements bystoring only certain portions of the content from within a sourcestream.

For illustrative purposes, FIGS. 1-8 describe a communications systemfor using a duplicating switch to stream data units to a terminal. Forbrevity, several elements in the figures described below are representedas monolithic entities. However, as would be understood by one skilledin the art, these elements each may include numerous interconnectedcomputers and components designed to perform a set of specifiedoperations and/or dedicated to a particular geographical region.

For illustrative purposes, FIG. 1 depicts a communications system 100that implements techniques using a duplicating switch to stream dataunits to two or more terminals. Communications system 100 may bestructured and arranged to include a source system 110, one or moreterminals 150, and communication software and hardware enablingcommunications between source system 110 and terminals 150. Moreparticularly, the communications system 100 typically includes thesource system 110, a network 120, a duplicating switch 130, a network140, and terminals 150. In actual implementations, the source system 110generally transmits one or more data units in a stream of data unitsacross network 120 to one or more duplicating switches 130, wherecontent from the data units is stored, duplicated and transmitted to oneor more terminals 150 through network 140 in an on-demand manner.

The source system 110 provides a stream of one or more data units acrossthe network 120 to the duplicating switch 130. Typically, the sourcesystem 110 is structured and arranged to convert a media source (e.g., avideo or audio feed) into data units for transmission across the network120. The source system 110 may include a general-purpose computer havinga central processor unit (CPU), and memory/storage devices that storedata and various programs such as an operating system and one or moreapplication programs. Other implementations of the source system 110include a workstation, a server, a device, a special purpose device orcomponent, other equipment or some combination thereof capable ofresponding to and executing instructions in a defined manner. The sourcesystem 110 also typically includes an input/output (I/O) device (e.g.,video and audio input and conversion capability), and peripheralequipment such as a display communications card or device (e.g., a modemor a network adapter) for exchanging data with the network 120.

Implementations of the source system 110 also may include a media systemthat transmits one of more pieces of media content across a network 120.For example, a source system 110 may transmit signals formattedaccording to European Telecommunications Standards Institute (ETSI),Digital Video Broadcasting (DVB), Advanced Television Systems Committee(ATSC), or European Cable Communications Association (ECCA) standardsacross a network to a cable head end. In another implementation, a cableprovider may transmit or direct video signals to a cable head end fordistribution in a cable network.

A communications link 115 is used to communicate data between sourcesystem 110 and network 120. Communications link 115 may include wired orwireless modes of communication, such as a telephone line, a wirelessnetwork link, a cable network, or a direct connection.

The network 120 typically includes hardware and/or software capable ofenabling direct or indirect communications between the source system 110and the duplicating switch 130. The network 120 may include a directlink between the source system 110 and the duplicating switch 130, or itmay include one or more networks or subnetworks between them (notexplicitly shown). Each network or subnetwork may include, for example,a wired or wireless data pathway capable of carrying and receiving data.Examples of network 120 include the Internet, the World Wide Web, WANs(“Wide Area Network”), LANs (“Local Area Networks”), analog or digitalwired and wireless telephone networks (e.g., PSTN (“Public SwitchedTelephone Network”), ISDN (“Integrated Services Digital Network”), orxDSL (“any form of Digital Subscriber Loop”)), radio, television, cable,satellite, and/or other delivery mechanisms for carrying data.

Generally, the duplicating switch 130 is structured and arranged tostore a received stream of data units for time-shifted transmission tomore than one terminal. Implementations of the duplicating switch 130may store one or more streams of data units. For example, theduplicating switch 130 may be capable of receiving a stream of IP(“Internet Protocol”) video and storing that video for subsequenttransmission. Implementations of duplicating switch 130 also may includehardware or software capable of transmitting or receiving media feedsnot resembling a stream of data units. For example, the duplicatingswitch may include a cable head end system that is capable of receivingor transmitting European Telecommunications Standards Institute (ETSI),Digital Video Broadcasting (DVB), Advanced Television Systems Committee(ATSC), or European Cable Communications Association (ECCA) fortransmission on a cable distribution system. The cable head end systemmay receive a satellite broadcast feed, convert the feed into a formatsuitable for storage, and thereafter convert the feed back to adifferent format for time-shifted transmission.

The network 140 generally includes one or more of links between theduplicating switch 130 and the terminals 150. For example, the network140 may include a direct physical link or a series of links connected byvarious pieces of network equipment. Generally, aspects of network 140may resemble aspects of network 120. For example, network 120 andnetwork 140 may share one or more hardware or software devices. Inanother example, networks 120 and 140 may use the same type of circuitsand/or equipment.

The terminal 150 may include one or more devices capable of receivingthe stream of data units transmitted by duplicating switch 130 throughnetwork 140. The terminal 150 may include a controller (not shown) thatprocesses instructions received from or generated by a softwareapplication, a program, a piece of code, a device, a computer, acomputer system, or a combination thereof, which independently orcollectively direct operations of the terminal 150. The instructions maybe embodied permanently or temporarily in any type of machine,component, equipment, storage medium, or propagated signal that iscapable of being delivered to the terminal 150 or that may reside withthe controller at the terminal 150. The terminal 150 may include ageneral-purpose computer (e.g., a personal computer) capable ofresponding to and executing instructions in a defined manner, aworkstation, a laptop, a PDA (“Personal Digital Assistant”), a wirelessphone, a component, other equipment, or some combination of these itemsthat is capable of responding to and executing instructions.

For instance, in one implementation, the terminal 150 includes one ormore information retrieval software applications (e.g., a browser, amail application, an instant messaging client, an Internet serviceprovider client, or an AOL TV (“America Online Television”) or otherintegrated client) capable of receiving one or more data units. Theinformation retrieval applications may run on a general purposeoperating system and a hardware platform that includes a general purposeprocessor and specialized hardware for graphics, communications and/orother capabilities. In another implementation, terminal 150 may includea wireless telephone running a micro-browser application on a reducedoperating system with general purpose and specialized hardware capableof operating in mobile environments.

In another implementation, the terminal 150 may include a simplifieddevice capable of receiving a video signal not encapsulated in atraditional data unit. For example, the duplicating switch 130 maytransmit a raw video feed formatted in accordance with specificationsset forth by, e.g., European Telecommunications Standards Institute(ETSI), Digital Video Broadcasting (DVB), Advanced Television SystemsCommittee (ATSC), or European Cable Communications Association (ECCA)for transmission directly to a cable tuner or television.

FIG. 2 illustrates a duplicating switch 200 structured and arranged toreceive a stream, store content from the stream, generate data unitsfrom the stream, and transmit the generated data units as a stream. Theduplicating switch 200 generally corresponds to the duplicating switch130 in FIG. 1. The duplicating switch 200 generally includes a storagesystem 210 for storing the stream of data units, a high speedinterconnect 220 between the various subsystems in the duplicatingswitch 200, a switching engine 230 for modifying and transmitting thestream of data units to two or more clients, a first communicationsinterface 240 for receiving a stream of data units from a source system,and a second communications interface 250 for transmitting a stream ofdata units to two or more clients.

The storage system 210 enables the duplicating switch 200 to store atleast the content portion of the data unit. The storage system 210 maybe volatile or nonvolatile and may include memory (e.g., RAM) and/orstorage (e.g., HDDS). Implementations of storage system 210 may includea hard disk drive or a more portable media, e.g., a compact disk, a tapedrive, or an optical memory device. Implementations also may includecombinations of memory and storage.

The high speed interconnect 220 generally refers to a device thatconnects a component of the duplicating switch 200 with other elementsof the duplicating switch 200. Examples of the high speed interconnect220 may include, but are not limited to, SCSI (“Small Computer SerialInterface”), Fibre Channel, UTOPIA (“Universal Test and Operations PHYinterface for ATM (“Asynchronous Transfer Mode”)), Infiniband, and otherprotocols and connection methods. The high speed interconnect mayinclude physical, logical, timing and electrical connections andstandards as well as protocols that enable these high speedinterconnects to exchange data.

Generally, a switching engine 230 includes a device that performsnetwork operations in hardware (e.g., a chip or part of chip). In someimplementations, the switching engine 230 may include an ASIC(“Application Specific Integrated Circuit”) implementing networkoperations logic directly on a chip (e.g., logical gates fabricated on asilicon wafer then manufactured into a chip). For example, an ASIC chipmay include a logical gate structure implemented in silicon andconfigured to receive a packet and filter based on examining an IPaddress.

Implementations of the switching engine 230 may include using a FPGA(“Field Programmable Gate Array”). An FPGA generally is defined as achip fabricated to allow third parties to implement a variety of logicaldesigns (e.g., group of gates) on the chip. For example, one designermay load a design that replaces the IP address of received IP packetswith a different IP address. Another example may include a design thatperforms segmentation and reassembly of IP packets as they are modifiedduring transmission of the IP packet through different networks.

Implementations of the switching engine 230 may include using a networkprocessor. A network processor generally is defined as a chip that,among other features, allows software to specify which networkoperations should be performed. One example of a network processor mayinclude several interconnected RISC (“Reduced Instruction Set Computer”)processors fabricated in a network processor chip. The network processorchip may implement on some of the RISC processors software that changean IP address of an IP packet. Other RISC processors in the networkprocessor may implement software that controls which terminals receivean IP stream.

The switching engine 230 may include a precoder (not shown) that isstructured and arranged to receive a data unit, extract a content piecefrom the payload portion of the data unit, determine where the contentpiece will be stored, and store the content piece in a structured mannerso that retrieval (e.g., playback) involves retrieving neighboringcontent pieces, packaging data units around the content pieces, andtransmitting the data units to one or more requesters. This process willbe described further with respect to FIG. 4.

The first communications interface 240 generally is structured andarranged to receive a stream of data units from a device such as thesource system 110. Implementations of the communications interface mayinclude a LAN or WAN interface with the ability to direct the data unitsto one or more locations in the duplicating switch 200, using, forexample, the high speed interconnect 220. Implementations also mayinclude other forms of transmitting a media signal, including ETSI, DVB,ATSC, or ECCA.

The second communications interface 250 generally is structured andarranged to transmit a stream of data units from the memory system 210to one or more devices that generally correspond with recipients, suchas terminal 150 described with respect to FIG. 1. Implementations of thesecond communications interface 250 may include a LAN or WAN interfacewith the ability to direct the data units to one or more locations inthe duplicating switch 200 using, for example, the high speedinterconnect 220. Implementations also may include other forms ortransmitting a media signal other than by IP networking. In addition,the second communications interface 250 is not limited to the same typeof format as the first communications interface 240, though they mayinclude the same format and even the same physical interface. Forexample, the first communications interface 240 may include a POS(“Packet-over-SONET”) interface while the second communicationsinterface 250 may include some form of Ethernet (e.g., 100-Base-T,Gigabit Ethernet).

FIG. 3A provides an exemplary block diagram of a duplicating switch(e.g., duplicating switch 130 in FIG. 1) with a memory implementation.The duplicating switch 300A includes a RAM array 320A, a switchingengine 330A and a network interface 340A.

The RAM array 320A may include one or more RAM memory banks structuredand arranged to store one or more pieces of content. The RAM array 320Amay store just a portion of the stream of data units. For example, aprovider streaming out a movie may store one portion of the movie forseveral users to watch at one time. The RAM array 320A may store awindow (e.g., a ten-minute window) of the movie that a user may use totime-shift the movie (e.g., pause, stop playing, or rewind) whilestaying current with the movie being broadcast.

Within the RAM array 320A, there may be location identifiers to keeptrack or indicate which content piece to package and/or transmit to aterminal. For example, an OSP (“Online Service Provider”) may schedule astream of data units to be transmitted to terminals at a certain time.In one example, the duplicating switch loads a portion of the stream ofcontent pieces indicated by the location identifier to the RAM array320A. In this example, the duplicating switch may use one or morepointers to indicate which content pieces (e.g., frames) should betransmitted to which user. In another example, an on-demand system mayload a larger portion of the content pieces to memory and may use afirst pointer to transmit one stream of data units and a second pointerto transmit a second stream of data units simultaneously or otherwise.

The switching engine 330A is structured and arranged to manage thecontent being stored in and retrieved from the RAM array 320A. Aspectsof the switching engine 330A generally correspond to aspects of theswitching engine 230 in FIG. 2. The switching engine 330A generallyloads and retrieves content to/from the RAM array 320A. Examples ofcontent that may be loaded and retrieved by switching engine 330Ainclude content pieces without wrappers (e.g., OSI wrappers), such asdatagrams having MPEG (“Motion Picture Experts Group”) I, P, and Bframes removed, video frames and differential checksum values thatdescribe frame-to-frame changes and frames with one or more addedwrappers (e.g., a layer 4 datagram). In one implementation, theswitching engine 330A may implement a system of pointers designed tokeep track of where in time or sequence number the terminals are withrespect to the available stored content. The switching engine 330A mayinclude a device, a program, a software controller, or another system ordevice in combination with the above. In another implementation, theswitching engine 330A may manage overall system utilization and refusesubsequent requests for services or attempt to serve more than oneterminal from one stream of data units.

The network interface 340A is designed to transmit and receive a streamof data units and generally corresponds to the first communicationsinterface 240 and second communications interface 250 described in FIG.2.

FIG. 3B provides another exemplary block diagram of a duplicating switch300B with a storage implementation. The duplicating switch 300B includesa stream platform 310B, a switching engine 330B, and a network interface340B.

The stream platform 310B is structured and arranged to store contentfrom within a stream of data units. The stream platform 310B includes ahard disk drive 312B (or a tape drive or other magnetic memory) andoptical memory 316B. Generally, the stream platform 310B includes memorycomponents with low bandwidth performance but high capacities. Forexample, storage may include solid-state-memory (not shown) that isslower than solid-state memory used in other applications. Typically,because of the greater storage available with less bandwidth, the streamplatform 310B will store a larger portion of a stream (e.g., a movie),but will limit access to fewer simultaneous streams absent RAM or othercache interfaces.

Implementations of the storage platform 310B may include the diskstorage 312B having a RAM interface to the switching engine 330B. Forexample, the duplicating switch may include a RAM bank and disk storage.Content pieces may be loaded to the disk storage such that the contentpieces are retrieved in the order that they are transmitted. As thecontent pieces are being retrieved, they are loaded to the RAM bank. Thehigher throughput performance of the RAM banks may enable more terminalsto access the same content piece. Terminals accessing the stream of dataunits may use a pointer to the content pieces in the RAM bank to keeptrack and load the data units they need in the stream of data units.

The switching engine 330B is structured and arranged to manage thecontent being stored and retrieved in the stream platform 310B. Theswitching engine 330B generally corresponds to the switching engine 330Adescribed with respect to FIG. 3A. The network interface 340B isdesigned to transmit and receive a stream of data units and generallycorresponds to the first communications interface 240 and secondcommunications interface 250 described with respect to FIG. 2.

The RAM-based and storage-based systems described with respect to FIGS.3A and 3B illustrate implementations that are designed to account forcommon limitations of the existing memory and storage systems (e.g.,solid-state RAM offers high throughput but less storage while harddrives and optical memory offer higher storage but less throughput).However, implementations are not limited to those shown, nor are memoryor storage devices necessarily subject to these constraints. Forexample, a disk drive may be used to implement a system managingmultiple pointers and may offer higher bandwidth, while solid-statememory may offer higher density storage than the disk drive storage.

FIG. 4 shows an example of a duplicating switch 400 with precoderfunctionality. The duplicating switch 400 generally corresponds to theduplicating switch 130 of FIG. 1. The duplicating switch 400 includes adata unit interface 410, a content extraction system 420, a contentarrangement system 440, and a content store 450.

The data unit interface 410 generally is structured and arranged tointerface with a network to transmit and receive a data unit from thecontent store 440. Generally, the functionality of the data unitinterface 410 corresponds to the functionality of the firstcommunications interface 240 and the second communications interface 250of FIG. 2. Data unit interface 410 also may be configured to segment andreassemble a data unit that has been separated during transmission, orto handle unconventional data units. For example, the data unitinterface 410 may be configured to transmit/receive one or more mediaframes (e.g., frames formatted according to one of ETSI, DVB, ATSC, orECCA). In one instance, if the duplicating switch 400 receives an analogsignal, the data unit interface 410 may convert the signal to arecognized format that the frame or content piece may store.

The content extraction system 420 is structured and arranged to remove adata unit wrapper that is added around content for transmission. Forexample, the content extraction system 420 may remove one or more bitsassociated with OSI (“Open Systems Interconnect”) informationencapsulated along with the content for transmission. The contentextraction system 420 also is capable of adding the wrapper when thedata is retrieved from the content store 450 for subsequenttransmission. For example, the content extraction system 420 may removewrapper information when storing a stream of data units in the contentstore 450 and may add a different wrapper when transmitting the streamof data units from the content store 450.

The content arranger 440 is structured and arranged to direct storageand retrieval of the content information such that the contentinformation may be retrieved in a determinate manner. For example, thecontent may be arranged so that the addressing information may beupdated in predictable increments. In another example, the content maybe arranged such that the difference between frames of content may becalculated by analyzing an associated checksum that then may be stored.

Determining where a content piece may be stored and storing the contentpiece may include using hard disk drive constraints to store the contentpiece. For example, the content store 450 (e.g., hard drive) may storethe content pieces such that the same “read” or data retrieval willretrieve related content pieces that are frequently transmitted in closeproximity to one another (e.g., adjacent frames in a movie or adjacentI, P, and B MPEG frames).

Determining where a content piece may be stored and storing the contentpiece may include using solid-state storage (e.g., various forms of RAM)to store the content piece. For example, the solid-state storage maystore all or a portion of the stream in an array of RAM memory. If aportion of the RAM memory is used to store the content piece, the RAMmay load a certain window of content for transmission to one or moreterminals. In some implementations, the duplicating switch may storemore than one instance of the stream of data units in the array of RAM.

The content store 450 is structured and arranged to store content piecesor frames. As described above with respect to the content arranger 440,the content is generally structured and arranged to be retrieved in amanner enabling transmission of related content pieces to one or moreterminals. The content store 450 generally corresponds to the memorysystem 210 of FIG. 2, the RAM array 320A of FIG. 3A, and the storageplatform 310B of FIG. 3B.

FIG. 5 illustrates a procedure 500 for storing and transmitting a dataunit using a duplicating switch. In general, the procedure 500 may beperformed using one of the duplicating switches described with respectto FIGS. 1-4.

Initially, the duplicating switch receives a data unit (step 505) andselects the content piece from the data unit (step 510). Typically,selecting the content piece of the data unit involves identifying fieldsor portions of the data unit that correspond to the content, andremoving some or all aspects not related to the content. For example, aduplicating switch may remove one or more layers of an OSI (“OpenSystems Interconnection”) header and store the remainder of the dataunit as the content piece. In another example, selecting the content mayinclude creating or modifying location identifiers to identify whichportion of the data unit should be stored when the data unit is loadedto memory.

Selecting the content may include enabling one or more portions of otheraspects of the data unit to be retained with the content. For example,one or more fields of the OSI header may be preserved and stored ascontent.

Implementations may include using a pre-coder to modify or adjust thecontent for storage. For example, the pre-coder may compress the contentso that less bandwidth is consumed during transmission. In anotherexample, the pre-coder may calculate a checksum or shortcut describingintra-content differences. This checksum or shortcut may be stored inplace of storing some of the content pieces.

The duplicating switch determines the location in the memory system inwhich to store the content piece (step 520). Typically, the location forstorage of the content piece is selected so that related content piecesmay be retrieved in related operations. Examples of related content mayinclude sequential frames in a video and/or content in a time slice. Theduplicating switch then stores the content piece in the determinedlocation (step 530).

At some later time, the duplicating switch receives a request for acontent piece (step 540). Receiving a request for a content piece mayinclude having a user (e.g., terminal 150 in FIG. 1) request a videostream for display on the user's home computer. Implementations also mayinclude having other devices request the content piece. For example, acable modem acting as a set top box may request a content piece fordisplay to a television.

Implementations also may include having a request originate from asource other than the intended destination. For example, a cable systemadministrator may generate a request for the content piece on behalf ofone or more subscribers.

The duplicating switch 130 determines which content piece has beenrequested (step 550). The requestor may designate a content piece tosend. For example, a terminal may keep track of which content has beenreceived, and may generate a request for one or more pieces of content(e.g., frame number 100 is missing). Implementations also may includehaving the duplicating switch track which content piece is required. Forexample, a duplicating switch may attempt to transmit the same contentpiece to several users.

The duplicating switch 130 determines where the content piece is located(step 560). To do so, the duplicating switch may use the locationidentifiers described with respect to FIGS. 2 and 3. Otherimplementations may employ a file and/or an archiving system maintainedto manage access to content pieces.

The duplicating switch 130 retrieves the content piece (step 570). Theduplicating switch may do so by reading a memory location specified by alocation identifier. Other implementations may include retrievingmultiple pieces of content information (e.g., reading a sector on adisk).

The duplicating switch 130 packages the content piece in a data unit(step 580). For example, the duplicating switch may add one or morelayers of OSI information (e.g., addressing information).Implementations where one or more aspects of the data unit other thancontent are stored with the content piece may include modifying one ormore parameters in those fields. For example, if an Internet Protocolpacket is stored, the destination address may be modified to theaddresses of requesting users.

Finally, the duplicating switch transmits the data unit to one or moreterminals (step 590). The data unit may be transmitted in formats otherthan IP addressing. For example, transmitting the data unit may includetransmitting an on-demand channel over a network.

The function of a communications system 600 will now be described withrespect to FIG. 6. Communications system 600 generally includes a sourcesystem 602, a manager 604, a duplicating switch 606, and terminals 608and 610. In general, the source system 602 corresponds to the sourcesystem 110 of FIG. 1, duplicating switch 606 corresponds to duplicatingswitch 130 in FIG. 1, and terminals 608 and 610 correspond to terminals150 of FIG. 1. The manager 604 may include a cable system operator, anOSP, a content provider, or an entity capable of providing instructionsor direction to the duplicating switch 606.

As shown, the source system 602 generates a stream of data units (step613). The source system 602 transmits the stream of data units to theduplicating switch 606 (step 616).

The duplicating switch 606 receives the stream of data units (step 625).The duplicating switch 606 then stores at least the content pieces fromthe stream of data units (step 627).

The stream may be transmitted in a variety of ways. In someimplementations, the manager 604 waits for a condition to occur (step618). For example, the manager may be a scheduler that is programmed todirect a duplicating switch “broadcast.” When the condition occurs (step620), the manager 604 transmits a request to the duplicating switch 606to transmit the stream of data units (step 623).

Alternatively, a terminal 608 may generate a request for a stream (step633). For example, the terminal 608 may generate a request to view aparticular video stream. The duplicating switch 606 receives the request(step 630).

In an implementation generally corresponding to the system describedwith respect to FIG. 3B, the duplicating switch 606 may load one or morecontent pieces into fast memory (e.g., RAM) (step 631). For example, theduplicating switch 606 may determine that there is inadequate bandwidthto the existing storage of the content and may load frequently-accessedcontent pieces to the faster memory to increase capacity.

Regardless of the mechanism used to indicate when to transmit the streamof data units to a terminal, the duplicating switch 606 may transmit thestream of data units to two or more terminals 608, 610 (step 636). Insome implementations, a terminal receives a stream that has beenbroadcast or otherwise automatically transmitted to the stream recipientwithout requesting the stream of data units. In either case, terminals608 and 610 receive the stream of data units (step 640 and 640A).Depending on the implementation, a different “stack” of content piecesmay be loaded into memory to support terminal 610.

In some implementations, the terminal 608 may generate and transmit apause message (step 645). For example, a terminal may wish to “pause” avideo on-demand stream and return to the stream at a later point. Whenthe duplicating switch 606 receives the pause message (step 650), theduplicating switch 606 pauses transmitting to the terminal 608 (step655). The duplicating switch 606 may still transmit a stream of dataunits to terminal 610 (not shown). The pause message may be implementedin a variety of ways. For example, terminal 608 may keep track of whichdata units have been received and resume where it left off by generatingand transmitting a resume message (step 660). Another example mayinclude having the terminal 608 transmit a stop message and theduplicating switch 606 keep track of where to resume when the transmitresume message is received (step 660).

If and when the duplicating switch 606 receives the resume message (step665), the duplicating switch 606 transmits the stream of data units 670to the terminal (step 670). The terminal 608 then receives the stream ofdata units (step 675).

FIG. 7A depicts a duplicating switch 700A structured and arranged tostore multiple instances of the stream of data units. The duplicatingswitch 700A transmits two streams of data units, stream A and stream A¹.Stream A occupies memory storage 710A in the memory bank, while streamA¹ occupies memory storage 720A in the memory bank. In oneimplementation, a first pointer 715A to the memory storage 710Aindicates which content piece, relative to other content pieces, shouldbe encapsulated as a data unit and transmitted to a terminal requestingStream A. As mentioned previously, implementations may include storing aportion of the content pieces in the memory bank. For example, ifproblematic network conditions prevent a terminal from receiving some ofthe stream of data units, the terminal may not receive some of thecontent pieces and may experience gaps in receiving the stream of dataunits (e.g., missing time in a movie).

A second pointer 725A to the memory storage 720A indicates whichportions of content pieces encapsulated in a stream of data units arebeing transmitted to several terminals. One or more terminals wishing toreceive one or more data units in the stream of data units receive thecontent piece corresponding to the second pointer 725A, which iscontinuously advanced to the next content piece. In someimplementations, the second pointer 725A may advance several contentpieces and encapsulate more than one content piece in a data unit.

FIG. 7B depicts a duplicating switch 700B structured and arranged tostore multiple location identifiers. In this example, duplicating switch700B includes five content pieces in stream A: A1 710,A2 720,A3 730,A4740, and A5 750. Duplicating switch 700B also includes an area of memoryallocated for an expected content piece A6 760.

In one example, the duplicating switch 700B enables each of terminals T,U and V to receive its own stream of data units. Each of the terminalsmanages a location identifier (e.g., pointer) to direct the duplicatingswitch to select the appropriate content piece to be transmitted. Forexample, terminals T, U, and V may begin by requesting content piece A1710 simultaneously.

After some content pieces have been transmitted, and as shown in FIG.7B, the location identifier 725 for terminal T may be referencingcontent piece A2 720, while the location identifier 742 and the locationidentifier 744 for terminals U and V are referencing content piece A4740 that corresponds to a different time-shift than content piece A2.This offset may have occurred because, for example, terminal T pausedreceipt of the stream of data units, and is now receiving content piecesthat are delayed relative to those received by terminals U and V.

In another example, duplicating switch 700B includes five content piecesin stream B: B1 770, B2 771, B3 772, B4 773, and B5 780. Duplicatingswitch 700B also includes an area of memory allocated for an expectedcontent piece B6 790. In one implementation, stream B may be part of thesame stream of data units as stream A, but may correspond to a differentportion of the stream of data units. For example, stream A may be a“video” stream 40 minutes into a video stream while stream B is fiveminutes into the same video stream. In another example, stream B may beidentical to stream A but was added to implement better systemperformance. In yet another example, stream A and stream B may representcompletely different video streams (e.g., two different televisionchannels).

FIG. 8 illustrates a procedure 800 for implementing a “Pause” functionon a duplicating switch, such as the duplicating switches described withrespect to FIGS. 1-7. Initially, the duplicating switch receives astream of data units (step 810) and stores content pieces from thestream of data units (step 820). With the content stored and ready fortransmission, the duplicating switch waits to receive a request to playthe stream of data units (step 830). Though the duplicating switch maywait for a request-to-play message, in some implementations, theduplicating switch may begin to transmit (e.g., play) upon receipt ofthe stream. In this configuration, the content might only be stored whena user requests pausing of the stream.

In an optional implementation, the duplicating switch may load thestream (content pieces) to fast memory (step 840). This generallycorresponds to loading the stream to fast memory as described withrespect to FIG. 6.

The duplicating switch transmits the stream of data units (step 850).While transmitting the stream, the duplicating switch 130 may receive apause request (step 860). If the duplicating switch 130 receives a pauserequest, the duplicating switch stops transmitting the stream of dataunits to the terminal (step 865). With the stream of data units paused,the duplicating switch 130 may wait to receive a play request (step870).

If the play request is received, the duplicating switch 130 continues totransmit the stream of data units where the terminal left off (step880). If not, the duplicating switch 130 waits for the resume request.When the terminal resumes receiving the stream of data units, theduplicating switch checks for a new pause request (step 860).

If the duplicating switch 130 does not receive a pause request, theduplicating switch may receive a stop request or reach the end of thestream (step 885). If the stop request is received or the end of thestream of data units is reached, the duplicating switch ceasestransmitting (step 890). If not, the duplicating switch 130 continuestransmitting and returns to waiting for a pause request (step 860).

Ceasing transmitting may include automatically selecting another streamof data units to be transmitted. For example, the duplicating switch 130may select another video to transmit when one video ends.

An “instant replay” or rewind feature may be created using a similarprocess, except instead of resuming transmission of a stream where thestream was produced, the stream is retransmitted time-shifted to anearlier moment in the stream (e.g., 30 seconds for a commercial, 15seconds for a sporting event). For example, the duplicating switch mayload content from memory representing the stream 30 seconds earlier, andmay transmit that content beginning at the earlier location (continuingon from that point).

Other implementations are within the scope of the following claims. Inparticular, in some implementations, the terminal includes a set toptuner set to receive an analog signal. Also, the location identifiersdescribed in FIG. 8 may be maintained on the client, or on a separateserver or device to indicate which content piece the terminals may bereceiving.

The source, network, on-demand-system, and terminal also may bedistributed across different entities in the communication system, andmay make use of one or more agents and/or proxies to perform certainfunctions.

1. (canceled)
 2. A method of streaming data units to a user terminal ata duplicating switch, the method comprising: receiving a stream ofcontent, wherein the stream comprises at least one network layer dataunit having a payload portion and an address portion; using theduplicating switch to store content; receiving a request from a userterminal for the content of the stored stream, wherein the requestincludes address information of the user terminal; in response to thereceived request, using the duplicating switch to duplicate the storedstream of content by: duplicating the stored stream of content;replacing an address portion in at least one data unit comprising theduplicated stream with the address information of the user terminal;forwarding the duplicated stream to the user terminal.
 3. The method ofclaim 2 wherein using the duplicating switch to store content includesstoring content that is temporally related to the data units that arebeing generated.
 4. The method of claim 2 further comprising using alocation identifier to indicate which portion of content is beinggenerated into the duplicated stream.
 5. The method of claim 4 furthercomprising using location identifiers to access the content time-shiftedas two different streams.
 6. The method of claim 2 wherein using theduplicating switch to store content includes storing more than oneinstance of the same portion of content.
 7. The method of claim 6wherein using the duplicating switch to store content includes storingadditional instances of the stream as demand for the content increases.8. The method of claim 2 wherein using the duplicating switch to storecontent includes storing content and associated header information. 9.The method of claim 2 wherein using the duplicating switch to storecontent includes storing a checksum describing the content.
 10. Aduplicating switch comprising: means for receiving a stream of content,wherein the stream comprises at least one network layer data unit havinga payload portion and an address portion; means for using theduplicating switch to store content; means for receiving a request froma user terminal for the content of the stored stream, wherein therequest includes address information of the user terminal; means forusing the duplicating switch to duplicate the stored stream in responseto the received request by: duplicating the stored stream of content;replacing an address portion in at least one data unit comprising theduplicated stream with the address information of the user terminal;forwarding the duplicated stream to the user terminal.
 11. Theduplicating switch of claim 10 wherein means for storing contentincludes means for storing content that is temporally related to thedata units that are being generated.
 12. The duplicating switch of claim10 further comprising means for using a location identifier to indicatewhich portion of content is being generated into the duplicated stream.13. The duplicating switch of claim 12 further comprising means forusing location identifiers to access the content time-shifted as twodifferent streams.
 14. The duplicating switch of claim 10 wherein meansfor storing content includes means for storing more than one instance ofthe same portion of content.
 15. The duplicating switch of claim 14wherein means for storing content includes means for storing additionalinstances of the stream as demand for the content increases.
 16. Theduplicating switch of claim 10 wherein means for storing contentincludes means for storing content and associated header information.17. The duplicating switch of claim 10 wherein means for storing contentincludes means for storing a checksum describing the content.
 18. Aduplicating switch comprising: a first communications interfacestructured and arranged to receive a stream of content, wherein thestream comprises at least one network layer data unit having a payloadportion and an address portion; a storage processor structured andarranged to store content; a second communications interface structuredand arranged to receive a request from a user terminal for the contentof the stored stream, wherein the request includes address informationof the user terminal; a duplicating processor structured and arranged toduplicate the stored stream in response to the received request by:duplicating the stored stream of content; replacing an address portionin at least one data unit comprising the duplicated stream with theaddress information of the user terminal; forwarding the duplicatedstream to the user terminal.
 19. The duplicating switch of claim 18wherein the storage processor is structured and arranged to storecontent that is temporally related to the data units that are beinggenerated.
 20. The duplicating switch of claim 18 further comprising afirst memory processor structured and arranged to use a locationidentifier to indicate which portion of content is being generated intothe duplicated stream.
 21. The duplicating switch of claim 20 furthercomprising a second memory processor structured and arranged to uselocation identifiers to access the content time-shifted as two differentstreams.
 22. The duplicating switch of claim 18 wherein storageprocessor is structured and arranged to store more than one instance ofthe same portion of content.
 23. The duplicating switch of claim 22wherein the storage processor is structured and arranged to storeadditional instances of the stream as demand for the content increases.24. The duplicating switch of claim 18 wherein the storage processor isstructured and arranged to store content and associated headerinformation.
 25. The duplicating switch of claim 24 wherein the storageprocessor is structured and arranged to store a checksum describing thecontent.
 26. The duplicating switch of claim 18 wherein the secondcommunications interface is structured and arranged to make at least oneof the duplicated stream available in response to receiving a requestfrom a terminal.